The present invention relates to noise suppression systems in receivers generally, and cellular radio communication systems in particular.
Conventional radio receivers are well known in the art, as well are many associated noise problems. Noise problems can be categorized into externally generated noise and internally generated noise. Externally generated noise is typically associated with interference from other radio frequency sources such as other radios, electrical equipment, etc. Internally generated noise is typically associated with thermal noise, electrical incompatibility between internal components, etc.
A major problem with the introduction of noise is that it degrades the signal clarity and can prevent the radio receiver from identifying and filtering out the desired signals. In fact, signal clarity decreases in direct proportion to the amount of noise. There are conventionally known techniques for reducing externally generated noise by, for example, using multiple antennas typically called a diversity configuration. Each antenna receives roughly the same externally generated noise, so the received signals are fed through a noise cancellation system to filter out the desired signal. While this method can cancel external noise it does not address internal noise.
Internally generated noise can often be difficult to identify and suppress. A leading source of internally generated noise is thermal noise that is generated within the radio receiver by components such as filters and amplifiers. Thermal noise is inherent in electronics and arises from the random movement of electrons within and between electrical components, which makes thermal noise difficult to identify and suppress. To date, conventional radio receivers have not provided efficient techniques for identifying and suppressing such noise.
What is needed is a technique for identifying and suppressing both external and internal noise while maintaining the integrity of desired the signal.
The present invention relates to noise suppression systems in receivers. Exemplary embodiments are provided for use in cellular radio communication systems, but the invention is applicable to any type of receiver.
A noise suppression apparatus for use in a receiver includes an input terminal adapted to receive an inbound signal. A channel splitter is coupled to the input terminal and configured to split the inbound signal into a substantially identical first signal and second signal. A first mixer coupled to the channel splitter and configured to receive the first signal, and a second mixer coupled to the channel splitter and configured to receive the second signal. A first local oscillator is coupled to the first mixer and configured to generate a first LO frequency signal, and a second local oscillator coupled to the second mixer and configured to generate a second LO frequency signal, where the first LO frequency signal and second LO frequency signal differ from one another. The first mixer is configured to mix the first signal with the first LO frequency signal to create a first mixed signal, and the second mixer is configured to mix the second signal with the second LO frequency signal to create a second mixed signal. A combiner is coupled to the first mixer and the second mixer and configured to combine the first mixed signal with the second mixed signal to create a noise suppressed output signal.
In one aspect of the exemplary embodiment, a reference signal generator is coupled to the first local oscillator and the second local oscillator. Bandpass filters may also be disposed between the mixers and the combiner to filter the first mixed signal and the second mixed signal. In another aspect of the exemplary embodiment, an analog to digital convertor is coupled to the input terminal, and the first mixer, second mixer, and combiner are structured in a digital signal processor.
Another exemplary embodiment of a noise suppression apparatus for use in a receiver, includes an input terminal adapted to receive an inbound signal. A mixer is coupled to the input terminal and configured to receive the inbound signal. A local oscillator is coupled to the mixer and configured to generate a LO frequency signal. The mixer is coupled to the first local oscillator and configured to mix the inbound signal with the LO frequency signal to create a mixed signal. A channel splitter is coupled to the mixer and configured to split the mixed signal into a substantially identical first signal and second signals. A combiner is coupled to the first mixer and the second mixer and configured to combine the first signal with the second signal to create a noise suppressed output signal.
In one aspect of the second exemplary embodiment, bandpass filters may also be disposed between the splitter and the combiner to filter the first signal and the second mixed signal to suppress noise. In another aspect of the exemplary embodiment, an analog to digital convertor is coupled to the input terminal, and the splitter, bandpass filters and combiner are structured in a digital signal processor.
Advantages of the invention include a high quality signal with an improved signal-to-noise ratio.